2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
P94 ECOTOxICOLOGICAL EVALuATION OF
ThE SLuDGES FROM wASTE wATER
TREATMENT PLANTS
HELEnA ZLáMALOVá GARGOŠOVá, LUCIE
HELLInGEROVá and MILADA VáVROVá
Institute of Chemistry and Technology of Environmental Protection,
Faculty of Chemistry, Brno University of Technology,
Purkyňova 118, 612 00 Brno, Czech Republic,
zlamalova@fch.vutbr.cz
Introduction
The tendency to improve the water quality in the Czech
Republic is linked with building up new waste water treatment
plants (WWTP), what results in growing production of
sewage sludges. Multi-purpose way for efficient utilization or
sludge disposal hasn’t existed till now.
Sewage sludges are very rich in nutrients and organic
matter. This makes the spreading of this kind of waste on
land as a fertilizer or an organic soil improver very suitable.
Unfortunately, the sludge tends to concentrate heavy metals
and organic compounds present in waste waters. The Sewage
Sludge Directive (86/278/EEC) regulates sludge use in such
way to prevent harmful effects on soil, vegetation, animals
and man. In the Czech Republic almost one third of sewage
sludges ends as a waste; this could be hazardeous. In Europe
hazardous wastes are classified by 14 criteria including
ecotoxicity (H 14). Environmental ecotoxicology deals with
the potentially harmful effects of chemicals and wastes on
organisms. For this purpose various testing organisms and
various type of bioassays are used.
The aim of our study was the ecotoxicological testing of
sewage sludges from different waste water treatment plants
by selected ecotoxicity tests with respect to their intended
use. We used following organisms: crustacea Daphnia magna
and Thamnocephalus platyurus and seeds of terrestrial plant
Sinapis alba. The values of 24h-LC50 and 48h-LC50 obtained
for Thamnocephalus platyurus and Daphnia magna and
72h-IC50 values gained for Sinapis alba are the basic data for
the ecotoxicological assessment of the sewage sludges and
for their classification following the Czech legislation 1,2 .
Experimental
Samples of sewage sludges from high-capacity municipal
WWTP, situated in Brno, Modřice and from small WWTP
in Veterinary and Pharmaceutical University Brno were
evaluated. From WWTP Brno, Modřice following sewage
sludges were tested:
•
•
•
anaerobic stabilized sewage sludges (AS)
dewatered anaerobic stabilized sewage sludges
(DWAS)
dessicated anaerobic stabilized sewage sludges (DSAS)
From local WWTP in Veterinary and Pharmaceutical
University Brno primary sludges were tested (PS).
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S a m p l e s P r e p a r a t i o n
All samples were collected in pure plastic bottle and untill
testing stored in the dark at 4 °C for less than four days prior
the bioassay experiment. Samples were dried at temperature
105 ± 5 °C and sludge dry residue was determinated gravimetrically.
Two types of water leaches were prepared from
studied sewage sludges. The first batch of samples was prepared
in accordance with Czech legislation; the samples were
mixed in ratio 1 : 10 (sludge dry residue: deionised water).
The second one was diluted with deionised water to have
the same dry matter content as anaerobic stabilized sewage
sludges from WWTP Modřice (3.89 %). Sample tubes filled
with defined quantity of sample and water were shaken at
5–10 rpm (revolutions per minute) for 24 hour at temperature
15–25 °C. After centrifugation the leaches supernatants were
removed and filtered using paper filter (5 μm). To assure suitable
surroundings for each testing organism the supernatants
were enriched by adding specific amounts of salts following
OECD Guidelines 3,4 .
P r i n c i p l e o f E c o t o x i c o l o g i c a l
T e s t s
The general principle of ecotoxicological tests is the
determination of effective concentration (EC50), eventually
lethal concentration (LC50) or inhibition concentration
(IC50). These concentrations of tested compound (substance,
sewage water or leaches of sewage sludges) cause the mortality
of 50 % of testing organisms or 50% inhibition of growth
rate in relation to control tests. The organisms are exposed
to the test substance for a period of 24, 48, and 72 hours in
agreement with requirements of a given test. At least five
test concentrations should be used. A stepwise procedure
involves three steps: the preliminary test, the confirmatory
test and the definitive test. The confirmatory test confirms or
disconfirms results of limit test. In preliminary test undiluted
sewage sludges leaches are used. If results of preliminary
test indicate possible ecotoxicity the definitive test follows.
The highest concentration in definitive test should preferably
result in 100% immobilization (mortality or inhibition) and
the lowest concentration tested should preferably give no
observable effect.
A p p l i c a t i o n o f E c o t o x i c i t y T e s t s
f o r S e w a g e S l u d g e s E v a l u a t i o n
Testing organisms (Daphnia magna, Thamnocephalus
platyurus, Sinapis alba.) were used in preliminary test with
raw water sewage leaches (WSL) and in definitive tests with
various testing concentrations of WSL; 50, 100, 200, 500,
700 ml dm –3 . Under the same conditions tests with control
group of the same organisms in standard freshwater but
without WSL were conducted.
The Daphtoxkit FTM makes use of the dormant eggs
of the crustaceans Daphnia magna, which are protected by
chitinous capsule called ephippium. Ephipia can be stored
for long time without losing their viability. When the testing
organisms are needed it is necessary to put chitinous capsule